Electrophotographic apparatus employing an elastic pressure pad for pressing the film against the photoconductor



y 1970 E. F. CIRIMELE ETAL 3,510,217 ELECTROPHOTOGRAPHIC APPARATUSEMPLOYING AN ELASTIC PRESSURE PAD FOR PRESSING THE FILM AGAINST THEPHOTQCONDUCTOR FiledFeb. 1o, i967 FIG. I

FIG. 2

INVENTORS EUGENE ECIRIMELE v ROY HL NBERG BY M 441 RNEY United StatesPatent 3,510,217 ELECTROPHOTOGRAPHIC APPARATUS EMPLOYING AN ELASTICPRESSURE PAD FOR PRESSING THE FILM AGAINST THE PHOTOCONDUCTOR Eugene F.Cirimele, Sunnyvale, and Roy Uhlenberg,

Mountain View, Calif assignors to Varian Associates, Palo Alto, 'Calif.,a corporation of California Filed Feb. 10, 1967, Ser. No. 615,257 Int.Cl. G03g 15/00; G03b 27/20, 29/00 US. Cl. 355-16 7 Claims ABSTRACT OFTHE DISCLOSURE In electrophotographic apparatuses, with aphotoconductive plate illuminated by a photon image, an elastic pressurepad holds the recording medium against the plate. The charge retentivesurface of an electrographic paper overlays the photoconductive plate. Apotential is applied across the photoconductive plate and electrographicpaper to deposit an electric charge image corresponding to the photonimage on the charge retentive surface of the electrographic paper. Thecharge image is subsequently developed by conventional methods employingelectrographic toner. During deposition of the charge image pattern, theelectrographic paper is pressed into nominal contact with thephotoconductive plate by means of an elastic pressure pad which has itssurface coated with a conductive paint for making electrical contactwith a conductive backing of the electrographic paper. The pressure padsare made of sponge rubber and having a thin non-porous skin which iscoated with conductive silver paint. The sponge rubber pad portion iscemented to a rigid backing plate. The pads are dome shaped to squeezethe air out between the paper and the photoconductive plate withouttrapping the air. The pads are preferably serrated to further preventtrapping of the air bubbles. Alternatively, the soft pressure padportion may be formed by a flexible plastic or rubber bag filled with afluid and coated externally with conductive paint.

Description of the prior art Heretofore, relatively rigid pressureplates have been employed fo pressing the charge retentive surface ofthe electrographic paper into contact with the photoconductive plate inelectrophotographic devices. The problem with this arrangement is thatsmall air gaps or bubbles are Summary of the present invention Theprincipal object of the present invention is the provision of animproved electrophotographic apparatus.

One feature of the present invention is the provision of a soft elasticpressure pad for pressing the charge retentive surface of anelectographic recording web into nominal contact with thephotoconductive imaging membe in an electrophotographic device, wherebyuniformity of contact between the web and the photoconductor is obtainedto assure uniformity in the formation of the charge image on the web.

Another feature of the present invention is the same as the precedingfeature wherein a flexible conductive coating is formed on the pressurepad formaking electrical contact with the back side of the recordingweb.

Another feature of the present invention is the same as any one or moreof the preceding features wherein the pressure pad is dome-shaped tofacilitate squeezing of air out of the spaces between thephotoconductive member and the web.

Another feature of the present invention is the same as any one or moreof the preceding features wherein the pressure pad is serrated toprevent trapping of large air bubbles in the spaces between the web andthe photoconductive member.

Another feature of the present invention is the same as any one or moreof the preceding features wherein the pressure pad is made of spongerubber with a thin nonporous flexible skin.

Another feature of the present invention is the same as any one or moreof the first three features wherein the pressure pad comprises a fluidfilled bag.

Other features and advantages of the present invention will becomeapparent upon a persual of the following specification taken inconnection with the accompanying drawings wherein:

Brief description of the drawings FIG. 1 is a schematic sectional viewof an electrophotographic camera embodying features of the presentinvention,

FIG. 2 is a view of a pressure pad portion of the structure of FIG. 1taken along line 22 in the direction of the arrows,

FIGS. 3 and 4 are views similar to that of FIG. 2 showing alternativepressure pads of the present invention.

Description of the preferred embodiments Referring now to FIGS. 1 and 2,there is shown an electrophotographic camera 1 embodying features of thepresent invention. The camera 1 includes a dark box 2 having a lens 3and shutter 4 at one end and a photoconductive plate 5 disposed, in thefocal plane of the lens 3, at the other end of the box 2. Thephotoconductive :plate 5 is supported from a glass plate 6 via theintermediary of an optically transparent metal electrode 7 sandwichedtherebetween. The plate asssembly, comprising glass plate 6, electrode 7and photoconductive plate 5, is cemented at its marginal edges to a dip8 .of the dark box 2.

A rear housing 9 covers over the rear side of the photoconductive plate5 and is hinged to the dark box 2 at 11. The rear housing 9 includes asupply roll 12 of electrographic recording paper 13, a strip of which isdisposed overlaying the photoconductive plate 5. The electrographicpaper comprises a thin film of dielectric coated on a conductive paperbacking. The dielectric film forms a charge retentive surface. The roll12 is mounted on a shaft 14 the ends of which are supported from theside walls of the rear housing 9. v v

A soft elastic pressure pad assembly 15 is disposed overlaying thephotoconductive plate 5 and the electrographic recording paper 13. Thepad assembly 15 is carried from a fixed shaft 16 by a plurality of leafsprings 17. The shaft 16 is supported at its ends from the rear housing9. A cam 18 is eccentrically mounted on the shaft 16 and a cam lever arm19 extends from the cam 18 out of the housing 9 through a slot 21therein. When the cam lever 19 is moved to the upper position, asindicated by the dotted lines, the cam 18 pushes the pressure padassembly 15 into engagement with the recording paper 13 and thephotoconductive plate 5.

The pressure pad assembly 15 includes a rectangular backing plate 25, asof 0.125" thick steel plate, to which is afiixed, as by cement, a softelastic pad 26, as of sponge rubber 0.563" thick. A thin flexible skin27, as of'non-porous rubber is bonded to and covers over the outersurface of the soft elastic pad such that the sponge material forms thecore of the pad assembly 15. A flexible electrically conductive paint28, as for example silver paint, type SC12 marketed by Micro-CircuitsCo., New Buffalo, Mich., is coated over the skin 27 for makingelectrical contact with a conductive backing on the electrographicrecording paper 13.

The pad 15 has a dome-shaped surface which abutts the paper 13 and whichis flattened when pushed against the photoconductive plate 5. Thepurpose of this domeshape is to permit the pressure pad 15 to squeezethe air, in the spaces between the paper 13 and the photoconductiveplate 5, outwardly from the center of the plate toward its edges as thepad 15 is pressed against the paper 13 and the plate 5. This preventsair bubbles from being trapped between the paper 13 and the plate 5.Such air bubbles prevent a nominal contact between the paper 13 and theplate 5 and, thus, prevent uniformity in the charge transfer to thecharge retentive surface of the electrographic paper 13.

To further assist in squeezing the air out of the spaces between thepaper 13 and the plate 5 without trapping air bubbles, the pad 15 isserrated by a pair of diagonally crossed slots 31. The slots 31 extendacross the pad from one corner to an opposed corner and pass through theskin 27 and core 26 to the plate 25. In a typical example, the slots 31are 0.125" to 0.063" wide.

The slots 31 provide line-shaped regions into which the trapped air canbe squeezed, thereby preventing large area bubbles of trapped air whichwould otherwise produce large blank areas in the charge images depositedupon the recording web 13.

Referring now to FIG. 3, there is shown an alternative pressure padassembly 32 which is essentially identical to pressure pad 15 of FIGS. 1and 2 except that the pad is serrated with a rectangular grid array ofslots 33. The slots 33 are spaced apart by approximately 1.5 to segmentthe pad into squares 1.5 on a side.

Referring now to FIG. 4, there is shown an alternative pressure padassembly 34 of the present invention. In this case, the pressure padcomprises a fiat dome-shaped bag provide the necessary air gap eventhough the two surfaces are pressed together. Thus, the term nominalcontact has been employed herein to describe the contact between the twosurfaces which permits the existence of a minute air gap on the order ofa few microns wide therebetween.

Once the recording paper has been pressed into nominal contact with thephotoconductive plate 5, the shutter 4 is opened to permit the photonimage, to be reproduced, to illuminate the photoconductive plate 5.Simultaneously, the timer switch 38 is activated for a certain exposuretime to apply the charge transfer potential across the photoconductiveplate 5 and the dielectric film of the recording paper 13. The appliedpotential causes a charge image, corresponding to the photon image onthe photoconductive plate 5, to be deposited on the charge retentivefilm of the recording paper 13. After the charge image has been formed,the timer 38 opens the circuit and the shutter 4 is closed. The operatorplaces the cam lever 19 in the lower position to release the pressure onthe paper 13 such that the exposed paper 13 may be pulled from thehousing 9 for subsequent development by conventional electrographictoner methods. Such methods include either those employing liquid toneror dry powdered toner.

Use of the soft elastic pressure pads 15, 32 or 34 assures a uniformnominal contact over the entire area of the photoconductive plate 5,thereby preventing large unprinted regions in the developed prints.

Although the pressure pad feature of the present invention has beendescribed, for simplicity of explanation, as it is employed in anelectrophotographic camera 1, it is equally applicable to otherelectrophotographic devices such as, for example, microfilm printers andradiographic cameras.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention can be madewithout departing from the scope thereof it is intended that all mattercon- 35 made of a flexible elastic skin, as of rubber, and filled with afiuid such as air or water. The bag 35 is cemented on one side to thebacking plate 25 and is coated on its other outside surfaces with aconductive flexible paint, such as silver paint, for making electricalcontact with the conductive backing of the electrographic recordingpaper 13.

Referring again to FIG. 1, a potential supply 36 suplies a negativepotential, as of 500 V., to one side of the photoconductive plate 5 vialead 37 and transparent electrode 7. A timing switch 38 is connected inthelead 37 for controlling the closed time of the circuit. The otherterminal of the supply 36 is grounded as is the backing plate 17 and padassembly 15.

, -In operation, the operator pulls an unexposed length of paper fromthe roll 12 past the photoconductive plate 5 such that the chargeretentive dielectric film layer of the electrographic paper 13 isdisposed overlaying the photoconductive plate 5. The operator then movesthe cam lever 19 to the upper position, indicated by dotted lines,'topress pressure pad assembly 15 against the paper 13 and, thus, thecharge retentive surface of the paper 13 into nominal contact with thephotoconductive plate 5.

1 According to the presently accepted theory for charge transfer to thecharge retentive surface of the paper 13, it is believed that a minuteair gap, on the order of a few microns, is required between thephotoconductive plate 5 and the charge retentive surface of the paper13. However, the photoconductive plate 5 and the thin, as of 4 micronsthick, dielectric charge retentive film of the paper havesurfaceirrigularities on the order of a few microns high. Thus, these surfaceirregularities are believed to tained in the above description or shownin the accompanying drawings shall be interpreted as illustrative andnot in a limiting sense.

What is claimed is:

1. In an electrophotographic apparatus, means forming a photoconductiveimaging member, means forming a electrographic recording web having athin dielectric charge retentive film formed on a conductive web, meansfor applying a potential across said recording web and saidphotoconductive member for depositing a charge image upon the chargeretentive surface of the recording web overlaying said photoconductivemember under the influence of the electrical potential applied acrosssaid photoconductive member and the recording Web, means for pressingthe charge retentive surface of the recording web against saidphotoconductive member, the improvement wherein, said means for pressingthe recording web against said photoconductive member includes a softelastic pressure pad disposed overlaying said photoconductive member andhaving a surface area overlaying said photoconductive member which issubstantially coextensive with the image area to be deposited on saidweb for pressing the charge retentive surface of the web against saidphotoconductive member over substantially the entire image area, wherebyuniform nominal contact is obtained between the charge retentive surfaceof the recording web and said photoconductive member, and said means forapplying an electrical potential across said recording web and saidphotoconductive member including a flexible conductive coating on thesurface of said soft pressure pad disposed overlying said electrographicrecording web for being pressed into electrical contact with saidconductive web portion of said recording web by said pressing means.

2. The apparatus of claim 1 wherein the pressure pad is dome-shaped tofacilitate squeezing of the air out of the spaces between saidphotoconductive member and the recording web.

3. The apparatus of claim 1 wherein said pressure pad is serrated in agrid pattern to prevent trapping of large air bubbles in the spacesbetween the recording web and said photoconductive member.

4. The apparatus of claim 1 wherein said soft elastic pressure padcomprises, a soft elastic core, and a flexible skin covering over saidelastic core.

5. The apparatus of claim 4 wherein said soft core is a spongy material.

6. The apparatus of claim 4 wherein said soft core is a fluid underpressure.

7. The apparatus of claim 1 including, means forming a backing platemember to which said soft elastic pres 15 sure pad is afiixed.

References Cited UNITED STATES PATENTS 7/1962 Audino 95-76 XR 8/1962Wight 9576 XR 12/ 1963 Alexander 95-1.7 12/1965 Jones 9576 11/1930 Crane355-92 6/1961 Sigler 355-94 10/1962 Walkup 355-3 U.S. Cl. X.R.

